1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display (LCD) device having a friction reducing layer. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving display quality.
2. Discussion of the Related Art
Until recently, display devices have generally used a cathode-ray tube (CRT). Presently, many efforts are being made to study and develop various types of flat panel displays, such as a liquid crystal display (LCD) device, a plasma display panel (PDP), a field emission display (FED), and an electro-luminescence display (ELD), as a substitute for CRTs. Of these flat panel displays, the LCD device has many advantages, such as high resolution, light weight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field into the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
FIG. 1 is a perspective view of an LCD device according to the related art.
As shown in FIG. 1, the LCD device 11 includes an upper substrate 5, a lower substrate 22 and a liquid crystal layer 14. The upper substrate 5 is often referred to as a color filter substrate that includes a color filter pattern 8, a black matrix 6 between the color filter patterns 8, and a common electrode 18 on both the color filter pattern 8 and the black matrix 6. The lower substrate 22 is often referred to as an array substrate that includes a data line 15 and a gate line 13 that cross each other and define a pixel region P. A pixel electrode 17 and a thin film transistor T as a switching element are positioned in each pixel region P. Thin film transistors T, which are disposed adjacent to where the data lines 15 and the gate lines 13 cross, are disposed in a matrix form on the lower substrate 22. The gate line 13 and a storage electrode 30 overlapping the gate line 13 define a storage capacitor C.
Though not shown in FIG. 1, upper and lower polarizers are disposed on outer surfaces of the upper and lower substrates 5 and 22, respectively. The polarizer transmits a component of light according with an optical axis of the polarizer. Accordingly, depending upon arrangement of the optical axes of the upper and lower polarizer, the LCD device 11 transmits or shuts light, thereby displaying images.
FIG. 2 is a cross-sectional view of a polarizer for the LCD device according to the related art.
As shown in FIG. 2, the polarizer 100 includes a polarizing layer 130 having an optical axis, first and second protecting layers 120 and 140 on lower and upper surfaces of the polarizing layer 130, respectively. Further, an adhesive layer 110 is disposed on a lower surface of the first protecting layer 120, and a protection film 150 is disposed on an upper surface of the second protecting layer 140.
The polarizing layer 130 transmits a light component according with the axis of the polarizing layer 130, and the first and second protecting layer 120 and 140 protect the polarizing layer 130. The polarizer 100 is attached to each upper and lower substrates 5 and 22 by the adhesive layer 110 (shown in FIG. 1). The protection film 150 protects the polarizer 100 from the outer environment, and is removed after attaching the polarizer 100 to each of the substrate.
After attaching polarizer 100 to each of the substrates, an outer case (not shown) is attached to the LCD device. In particular, the outer case covers side portions and lower portions of the LCD device, and thus an upper portion of the LCD device, which is the second protecting layer 140, is exposed.
Since the upper surface (i.e., the exposed surface of the second protection layer 140) is rough, a friction force is generated when the upper surface of the second protection layer 140 contacts an exterior object, for example, a finger. The friction force causes an abnormal variation of liquid crystal arrangement, and thus a light luminance is changed. In particular, when the LCD device is operated in a Normally Black Mode, a light leakage can be generated due to the friction force. Therefore, display quality can be degraded.